proxy.rs: expose set_passthrough_mode/vt_render_pending test hooks, and
on Drop only reset attribute state (fg/bg/hyperlink) instead of also
clearing the viewport — so the child's final output stays on screen like
a normal CLI once the palimpsest bug is fixed.
integration_tests.rs: tests asserting passthrough mode forwards child
PTY bytes verbatim (no termwiz re-encoding) and skips the deferred
render path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
adam
3492b2b1c5